I know there are several threads around this general issue, but even the suggested solutions don't yield the result I'm looking for. I would like the crop ratio to remember its last setting. Or, let me force a default, and keep that setting. Either would be great. The only answers I can find rely on Autosync, or copying the crop across all the images. Either are not really what I am looking for. Surely, there must be a way to force a default, other than "as shot".

The default crop ratio IS "as shot". It cannot be changed. And, really, I don't think you would want it to. It would be rather haphazard to let Lightroom decide which part of the image to crop, don't you think?

But I have had situations where I want ~100 images cropped to a ratio to suit a projector with 'all images full screen' slideshow.

I must (and do!) review every image to check that I have not cropped away important parts of any image.

So using Auto-Sync the Crop does save many, many mouse clicks in the Develop/Crop module for multiple photos. A quick scroll through the images in Loupe view to check them is much faster.

Even if I Auto-sync the crop, I still have some control on how I place the crop (in the viewed photo) knowing the typical subject matter in the images. eg. I might crop to the lower portion of the frame if I know I can lose some sky in all the photos.